The present invention is directed to catalytic steam reforming of a hydrocarbon feed stock by contact with catalysed hardware.
The term xe2x80x9ccatalysed hardwarexe2x80x9d as used herein refers to a catalyst system, where a layer of catalyst is placed on a surface of another material, e.g. a metal. The term porous structure stabilised catalysed hardware refers to a catalyst system, where a porous structure made from a material, which is stronger than the catalyst, is adhered to the other material and the catalyst is deposited in the cavities of the porous structure. In the remaining part of the description the porous structure is considered to be made from metal. However, any porous material, which is stronger than the catalytic material, can be used.
State of the art steam reforming technology makes use of reforming catalysts in form of pellets of various sizes and shapes. The catalyst pellets are placed in fixed bed reactors or reformer tubes. The overall steam reforming reaction is endothermic. The necessary heat is supplied from the environment outside the tubes.
Use of reformer tubes with catalysed hardware steam reforming catalysts on inner tube wall of a steam reforming reactor is disclosed in EP Patent Application No. 855,366. The main advantages of utilising catalysed hardware in the steam reforming process are:
a. Improved heat transport from the heat source outside the reformer tube to the catalyst because of the direct conduction of heat from the inner tube wall to the catalyst;
b. Reduced tube temperature resulting in increased lifetime and/or reduced tube material consumption;
c. Increased catalyst temperature resulting in increased catalyst activity, increased hydrocarbon conversion and reduced catalyst amount; and
d. Reduced pressure drop.
A general problem with catalysed hardware for use in steam reforming is to establish sufficient adhesive strength of the catalyst to the reactor wall, and at the same time retain the necessary properties of the catalyst with respect to catalytic activity, pore structure, sintering stability etc.
The object of the present invention is to provide catalysed hardware having improved adhesion stability together with required properties of catalytic performance in steam reforming processes.
In accordance with the above object, this invention is a process for the preparation of hydrogen and carbon monoxide rich gas by steam reforming of a hydrocarbon feedstock in the presence of a steam reforming catalyst having a porous supporting structure and being adhered to wall of a reforming reactor, wherein the steam reforming catalyst is deposited in the supporting porous structure.
Porous metal structures have improved adhesion to a metallic reactor wall. The catalyst is deposited within the porous metal structure and is retained in the structure, which reduces or even eliminates the requirement of adhesion of the catalyst to the reactor wall.
When practising the invention any type of metallic porous structure being able to withstand the actual process conditions used in the steam reforming process may be used, including metal foam, metal net, expanded metal, sinter metal and metal gauze. The requirement to the adhesion of the catalyst depends on the type of porous metal selected.
Foamed metal has a structure, where cavities of pores are substantially spherical and the openings of the cavities have a smaller radius than the radius of the spherical cavities. Catalytic material being deposited in the cavities cannot escape from the cavities. Adhesion of the catalyst to the metal is therefore not required.
The catalyst can be deposited in the cavities e.g. by intrusion of slurry containing a ceramic precursor into the metal foam, followed by drying, calcination, and impregnation of the active catalytic material.
If a porous metal structure is selected, in which the catalyst is not retained by the physical surface of the structure, the required adhesive strength of the catalyst to the metal is still reduced. Due to the increased catalyst/metal interface surface area the adhesive strength per unit area is lower in order to provide the same overall adhesive strength.
Attrition loss of the catalyst is advantageously reduced since the catalyst is protected by the metal structure when in contact with gas inevitably containing particles flowing along the reactors inner surface.
The risk of catalyst flaking off from the reactor wall due to e.g. thermal stress is considerably reduced.
Use of metal foam provided with a catalyst adhered to wall of a reactor vessel is disclosed in Japanese Patent Application No JP 59-205332(A) for the production of olefins from hydrocarbon feed stock. The purpose of this catalyst is to eliminate risk of coke formation when producing olefins with internal heat pyrolysis of heavy oil by using a catalyst lyst a cracking function for heavy substances. The above patent publication is completely silent about the procedure by which the catalyst containing foam is attached to the reactor vessel.
The porous structure for use in the inventive process is in a first step attached to the wall of the reaction vessel. Subsequently, the catalyst is dispersed in the porous structure.
The advantages of using catalysed hardware for steam reforming described above are in particular related to steam reforming processes and in general to endothermic processes being heated by external heat supply.
The porous metal can be adhered to the reactor wall by e.g. soldering or diffusion bonding.
The preparation step in which the porous metal is adhered to the reactor wall requires heating of the reactor and the porous metal to a temperature above the maximum operating temperature of the reactor. This is necessary to provide sufficient adhesion strength at the maximum operating temperature of the reactor.
When soldering is applied, the soldering temperature must be at least 100-150xc2x0 C. higher than the maximum operating temperature.
The catalyst can be arranged in the porous structure by means of e.g. spraying, painting or dipping into a slurry containing a ceramic precursor. Thereafter, the slurry is dried and calcined. Finally, the ceramic layer thus obtained is impregnated with the catalytic active material. Alternatively, the catalytic active material is applied simultaneously with the ceramic precursor.